A Giant Squid Genome Reveals the Unexpected

​Significant clues regarding the anatomy and development of the enigmatic giant squid have been unveiled from a genome sequence.

New research about the giant squid, scientifically known as Architeuthis dux​, was conducted by a University of Copenhagen team that includes scientist Caroline Albertin of the Marine Biological Laboratory (MBL), Woods Hole.

Some Other Process was Involved

Giant squids are hardly ever seen and have never been captured and kept alive, which means that their biology and the process of reproduction is still a puzzling matter. The genome part can, however, offer some significant insight.

“In terms of their genes, we found the giant squid look a lot like other animals. This means we can study these truly bizarre animals to learn more about ourselves,” says Albertin, who led the team that sequenced the first genome of a cephalopod (the group that includes squid, octopus, cuttlefish, and nautilus), back in 2005.

With Rute da Fonseca as the lead, the team found that the creature’s genome is massive, with probably 2.7 billion DNA base pairs, with approximately 90 percent the size of the human genome.

Albertin observed numerous ancient, renowned gene families in the giant squid, comparing the four other cephalopod genus that has been sequenced, as well as with the human genome.

She discovered that some significant developmental genes in the majority of the animals existed in single copies in the giant squid genome. That means that the creature did not get so massive due to the whole-genome duplication. Knowing the way this species of the giant squid got to be so big requires further analysis of its genome. So, knowing how this squid species got so giant awaits further probing of its genome.

“A genome is a first step for answering a lot of questions about the biology of these very weird animals, such as how they acquired the largest brain among the invertebrates, their sophisticated behaviors and agility, and their incredible skill at instantaneous camouflage,” Albertin said.

“While cephalopods have many complex and elaborate features, they are thought to have evolved independently of the vertebrates. By comparing their genomes, we can ask, ‘Are cephalopods and vertebrates built the same way or are they built differently?'”

Unexpected Findings

Albertin also discovered over 100 genes in the protocadherin species in the giant squid genome, something that is usually not present in abundance in invertebrates. 

“Protocadherins are thought to be important in wiring up a complicated brain correctly,” she says. “They were thought they were a vertebrate innovation, so we were really surprised when we found more than 100 of them in the octopus genome (in 2015). That seemed like a smoking gun to how you make a complicated brain. And we have found a similar expansion of protocadherins in the giant squid, as well.”

Finally, the scientist analyzed a gene family that, until now, is unique to cephalopods, known as reflectins.

“Reflectins encode a protein that is involved in making iridescence. Color is an important part of camouflage, so we are trying to understand what this gene family is doing and how it works,” Albertin says.

“Having this giant squid genome is an important node in helping us understand what makes a cephalopod a cephalopod. And it also can help us understand how new and novel genes arise in evolution and development.”

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